Resistor units and method of making the same



March 20, 1956 A. P. CHARBONNEAU RESISTOR UNITS AND METHOD OF' MAKING THE SAME Filed DeC. 4, 1952 2 Sheets-Sheet l March 20, 1956 A. P. CHARBONNEAU 2,739,214

RESISTOR UNITS AND METHOD OF MAKING THE SAME Filed Dec. 4, 1952 2 Sheets-Sheet 2 ./IOE`I United States Patent C Cutler-Hammer, Inc., Milwaukee, Wis., a corporation of'Delaware Application December 4, 1952, Seriai No. 324,078

11 Claims; (Cl. 2014-69) This invention relates'to resistor units and parts-therefor, particularlyresistor units ofthe type having stackedgrid elements, and to a method of making the same.

Inresistor: units of this type there is appreciable expansion'of. the resistance grids and of the members upon which the grids are mounted. An object of my invention isto providea resistor unit and a method of making the same in which such expansion is permitted without any buckling of the grids and further without distortion of the mounting structure 'for the unit.

Another object is to provide such a unit in which heating and consequent expansion ofthe members upon which the-grids are mounted is minimized.

Afurther object is to provide such a unit, and-a novel methodof making the same, in which the foregoing objects eandadvantages together with. ruggedness and `dep'endabilityV ofrthe unit may be achieved at .a minimum manufacturingcost.

These objectsand'advantages and others which will hereinafter appear are realized by the employmentof a gridofnovel construction which permits stacking of such grids in a manner permitting adequate cooling thereof withoutr excessive heating of the grid supports, and by the provision'o novel .mounting means permitting lengthwiseexpansionl of the vgrids and endwiseexpansion ofthe grid supports.

The accompanying drawings'illustrate an embodiment ofthe inventionwhich `will now be described, it'being understood that the embodiment shown is susceptible of variousmo'dicationsin respect of structural details without departing from the scope of the appended claims.

.ln the drawings:

.Figure l is 'a View in front elevation of a resistor unit embodying the invention;

Fig. 2 is an enlarged View in elevation of a oatingmountingplate;

Fig. 3 isan end elevational view'oi` the unit yshownin Fig.; 1; Y

Fg.l4 israfview in elevation of a preferred form ofthe resistor gridV employed;

Fig. 5 is-a view in elevation of several resistor'grids priory to inished' assembly, the respective end lugs-'of each .grid being bent in opposite directions, along the lines shown at X-X, in Fig. 4.

'Referringto'Figs 1 and 3 of the drawings, there-is shown a resistor unit of the type having stacked like resistor grids mounted upon parallel, spaced,;insul'ated rods, for vwhich rods a supporting frame is provided.

Oneof the like 'grids 1l) is shown in side elevationin Fig. 4, the same having a flat body portion 1li@ comprising astripforming 'a series of closely spaced, oppositelyA projecting,l parallel loops to form a relatively long, circuitous resistance path of substantially uniform cross sectional area.v The body' portion 1I)au bridges apairof lugs 10b,

2 perforationsll lies wholly outside the body portionforfa reason to be hereinafter set forth.

Each grid 10 consists of v an integral element'punched from a sheet of suitable, resilient, resistance material such, for example, as nickel chromium, copper nickel, or chrome from alloys.

Referring again to Fig. l, the grids 10 are-mounted upon insulatingrtubesll and `13r which in turn are mounted upon support rods'14 andV `15-respectively. Rod 14 and itstube 12iare `insertedthrough the perforationk 11 of one lug of each of the grids 10, and rod 15 and its tube 13 -are inserted through the perforation 1.1 of the other lug of each ofthe said grids. By the useiof 4spacers 16and insulatingwashers 19 between successive pairs of lugs, the grids 10 4are stacked in zigzag fashion to provide a continuous resistance path through thegridsrv As shown in Fig. l the respective pairs of adjacent lugs 10b are `pressed toward each-.other to aiford-.a good electricalconnection therebetween. The opposite end grids, which aredesignated 10X and 10S', have theirrcspective terminal .lugs 1Gb pressed into good electrical engagement with the terminals 22, 22. The insulating washers 19 serveto insulate from each other the successive connected pairs of lugs lb at the upper and lower ends of the unit shown in Fig. l.

Each of the terminals 22 is mounted upon tube 13 and is lstacked alongwith the grids 10, spacers 16 and insulators` 19. Terminals 22-are respectively provided -wi'th conductor attachingmeansof suitable form, as indicated at 22a.

In addition, successive `grids are arranged inA reverse relationship so thatthe body portions otne''esp,ec`t'ivesuc-Y cessivegrids aremounted on opposite sides of-a transverse plane which, inFig.. 3, bisects rods 12 and'13.

The rods 12 and 13 are each longer than their respective insulating tubes I4 Vand liso that both ends of Veach reatendfbeyond its yrespective tube. The exposed end rods are threaded. The stacked grids 1l) and the spacersfl and washers 19 arey firmly held in position on the tubes at each rod end aninsulating washer 19, a compression ,Washer.2l,,a tube retaining washer 25, a lock washer 26,

anda nut r2.7.' The nuts 27 are turned up tightly sov that a good electrical connection is provided at the pressure joint between each pair of adjacently mounted lugs. If desired "the lugs of eachdpair maybe welded together to insure a good electrical connection between them.v

If the grids, before assembly, lare atso that the-lugs lie intheplane of the body portion, las in the grid illustrated iti-Fig.. 4,.tigh`tening votnuts 27lwi1l deform the gridsso that each will`h`ave a double bow. kAfter heatingv of theA resistor, which will occur in testingjor in normal use of the unit, the resistors will take a permanent'` set and havethe normal assembled shape shown in Fig. ll. v

When vthe gridsare formed from heavy gauge mate rial,- the electrical gconnectionvat Athe pressure joint of adjacent grid lugs .will be-improved by bending thelugs vatan angleY-witlrthe.plane of the grid. The lugs are bent in opposite directions, alongV the lines X-X of Fig-4, so that -theylie inV parallel planesrforming similar angles with theplane o f-the'body'portion.4 Also, the angle formed by each` lug,issomewhat:greater thanthe angle at which the lug will be held when the stack is tightly assembled. l

This isvillustra'ted in Fig'S where the bodyportions of grids 30"and vtheir respective lugs 303, SGU'are shownin their relativeassembledpositions prior to the clamping togethen'of the'lugs.A The'latter areoppositely'bent from their respective Abody/"portions at an angle so that "the-'lugs form `an` angle lvvithioneanother from'that end-of each nearest its body'p'ortion. Upon tightening of the mou-ntlugs 60 and'llb will be-fpressed f toward each-'fother' to 3 Y provide a pressure joint, the maximum pressure in which joint will occur at the ends of the lugs nearest theirrespective body portions since the grids are formed of resilient material. Thus a good mechanical and electrical connection is insured and the current, in ti'owing'between successive grids 39, has a path of greatest area at the lugs, and the resistance variation'and consequent heating at the joint are minimized. Y

Stacking the grids in zigzag fashion,` with successive grids reversed as described, has the advantage that the respective body portions of the grids are widely separated for improved heat dissipation without the need for conducting spacers between lugs, which would double the number of pressure connections, Also the need for oiset lugs or long leads from the lugs to the resistor body is obviated. Such stacking, and its consequent advantages, is permissible because of the novel good shape in which the body of the grid bridges its lugs in such manner that the body portions of successive grids when reversed cannot make contact even though the lugs are not o'fset g,

or spaced. Moreover, the grid shape is such that both edges have like contour, except for minor variation in loop slots, thus permitting the grids to be punched from a strip Yof suitable resistance material with a minimum of waste.

The rods 12 and 13 are supported bythe end panels 34 and 35 of the box or frame comprising, in addition, four tie rods or bolts 36 extending between the respective corners of the end channels to hold the latter in fixed spaced relationship as by means of inner and outer nuts 50, 50 and a lock washer 51. To prevent buckling of the grids due to their endwise expansion, rod 15 only is xedly attached to the end channels 34 and 35; the other rod 14 V74,heinlgprgovided withV a oating mounting. The threaded ends of rod 15 are secured by nuts 37 and lock Washers 38 in openings near one edge of channels 34 and 35. Near the opposite end of each channel there is attached, by welding or otherwise, one of a pair of plates 39 having perforations 4i), asbest illustrated in Figs. l and 2.

The plates 39 are so positioned and welded or otherwise secured to the channels that, with the grids secured on the rods and with rod 15 secured in position by nuts 27 and 37, each end of rod 14 is disposed within one of the perforations 40. The latter are elongated in the plane bisecting said rods. Thus shaped, the perforations do not permit substantial lateral movement of rod 14 with respect to said plane, but do permit motion of rod 14 to vary the degree of separation of the rods as an incident to lengthwise expansion or contraction of the grids.

The rod 14 is of sutiicient length to extend between both of the perforations but has a length slightly less than the distance between the channels 34 and 3S. The channels prevent excessive endwise motion of rod 14 but do permit a degree of endwise expansion thereof'as an incident to heating of said rod. Y l

Provision is made for endwise expansion of rod 1S by cutting or slitting, at laterally spaced points 43, 43, one or both ofthe end channels 34, 35 to form a resilient tongue or tab'portion- 42 to which the rod 15`is rigidly attached,

as shown in Fig. 3. The tongue 42 holds rod 15 rigidly thereto but permits endwise expansion of said rod, inasmuch as tongue 42 may be bent out of the plane of the channel 34. As will be understood, the resilient tongue formation may be provided by cutting or slitting the channel or channels in various alternative ways.

I claim:

l. An electrical resistance unit comprising a pair of parallel spaced insulating rods, a plurality of resistor grids each having a pair of mounting lugs and a central body portion bridging said lugs, said plurality of resistor grids being stacked in zigzag fashion between said rods and secured thereto in such a manner that the body portions of successive grids lie on opposite sides of the plane of said rods, a support for said rods comprising a pair of end members positioned in fixed spaced relation, each of said members having secured thereto one of an opposed pair of attachment plates each having a perforation elongated in the plane of said rods to slidably engage an associated end of one of said rods, each of said members further having means for attaching thereto an associated end of the other rod.

2. A resistance unit according to claim l, in which at least one of said pair of end members is provided with slits adjacent and on opposite sides of said means for attaching its associated end of said other rod to permit movement of a portion of said member as an incident to linear expansion of said other rod without aiecting the spacing of said end members.v

3. A resistance unit according to claim 2, in which said resistor grid lugs are bent and have resilience tending to separate the outer ends of adjacent lugs, together with clamping means to prevent such separation.

4. An electrical resistance unit comprising a plurality of resistor grids each having a pair of mounting lugs and a central body portion bridging said lugs, said resistor grids being stacked in zigzag fashion with each grid, other than the end grids, having one lug in juxtaposed conductive relationship with one lug of the next succeeding grid and the other lug in juxtaposed conductive relationship with one lug of the next preceding grid, the body portions of successive grids being reversed and lying on opposite sides of a transverse plane.

5. For a resistor comprising a plurality of resistor grids stacked between parallel support rods, a resistor support comprising a pair of end members having fixed spaced relation, means for attaching one of said rods to the respective end members, and an opposed pair of members each attached to one of said end members and having a perforation elongated in the plane of said rods to slidably receive an associated end of the other'oi:- said rods, said fixed spacing ci said end members being somewhat greater than the length of said other rod, whereby the latter is free to move in said elongated perforation as an incident to expansion of said grids and endwise expansion of said rod last mentioned.

6. A device of the character set forth in claim 5, in which at least one of said pair of end members is provided with a flexible portion associated with said attaching means to permit linear expansion of said other rod without affecting the spacing of said end members.

7. In a resistance unit comprising a plurality of stacked resistor grids, a pair or support rods for supporting said grids, a pair of end members having spaced relation, means for attaching one of said rods to the respective end members, at least one of said end members being provided with a exible portion associated with said attaching means to permit linear expansion of said rod without aiecting the spacing of said end members.

8. The method of making an electrical resistance unit assembly of the type having stacked resistor grids mounted upon and extending between parallel insulated support rods, comprising `the steps of punching a plurality of individual grids with perforated end lugs from resilient sheet resistance material, bending the end lugs of each grid oppositely out of parailel with said grid so that the corresponding ends of the grids are bent in like direction from their respective body portions, the angle formed in each case being greater than the angle required after assembly of the unit, stacking the grids in zigzag fashion with one of said rods inserted in each of the perforated lugs of said grids and compressing and clamping the lug ends of said stacked grids whereby said lug ends are held in parallel planes.

9. The method of claim 8 in which said successive grids are stacked in reversed relationship with respect to the plane of said support rods.

10. An electrical resistance unit comprising a pair of parallel spaced support rods, a plurality of punched resistor grids each having a pair of mounting lugs mounted on said support rods respectively and a central body portion bridging said lugs, said resistor grids being stacked in zigzag fashion with the body portions of successive grids extending between said rods at angles of like degree on opposite sides of a plane perpendicular to the axes of the rods and with each grid, other than the end grids, having one lug connected in conductive relationship with one lug of the next succeeding grid and the other lug connected in conductive relationship with one lug of the next preceding grid, the body portions of successive grids being reversed and lying on opposite sides of a l0 transverse plane.

l1. An electrical resistance unit assembly comprising a plurality of punched resistor grids each having a pair of end mounting lugs and a body portion extending between said lugs and laterally therefrom, and a pair of 15 parallel mounting rods spaced outwardly of the body portion of said grids, said lugs being so secured upon said rods that the grids are stacked in zigzag fashion with the body portions of successive grids extending between said rods at angles of like degree on opposite sides of a plane perpendicular to the axes of the rods and with the body portions of successive grids on opposite sides of the plane of said rods.

References Cited in the file of this patent UNITED STATES PATENTS 1,162,788 Lindquist Dec. 7, 1915 1,860,493 Campbell May 31, 1932 1,890,780 Gray Dec. 13, 1932 1,933,532 Nichols Oct. 31, 1933 2,128,222 DuBois Aug. 30, 1938 

